A conventional altitude display for a terrain awareness warning system (TAWS) for a given aircraft provides a pilot with a visual display of the terrain having an altitude higher than the aircraft, as well as the terrain within some distance, usually 2000′, below an aircraft.
Referring to prior art FIG. 1, an environment is shown in which a conventional altitude display could be important. In situation I, an aircraft 12 is flying at an altitude X along a direction vector 16. In situation II, an aircraft 12′ is flying at an altitude X′ along a direction vector 16′. In situation III, an aircraft 12″ is flying at an altitude X″ along a direction vector 16″. Finally, in situation IV, an aircraft 12″′ is flying at an altitude X″′ along a direction vector 16″′. The aircrafts 12, 12′, 12″, and 12″′ are flying with direction vectors 16, 16′, 16″, 16″′, respectively, such that an obstruction 14 having height Y is within a forward arc, centered on the respective direction vector, as monitored by the conventional altitude display aboard each respective aircraft.
Starting by considering situation IV, a conventional altitude display would typically give a visual signal as the height Y of the obstruction 14 is greater than the altitude X″′ of the aircraft 12″′. In other words, X″′≦Y. An audible alert may be given as well if suitable criteria regarding time-to-impact of the terrain feature are also met. In all cases, the height Y and altitude X″′ may be measured by radio height, altitude above sea level, or other means, and preferably the same type of measurement, is employed for both distances. The visual signal in this situation would typically be a red area, such as a spot or square, on a cockpit display. The term ‘RED’ is shown in the figure to denote the range of operation which would result in a red area being displayed. The red area would be indicated to be at a range Z and at a bearing corresponding to the direction of the obstruction 14 relative to the centerline of the aircraft 12″′.
In situation III, a conventional altitude display would also typically give a red visual signal as the height Y of the obstruction 14 is within a predetermined elevation buffer “D” and within a predetermined time-to-impact from the altitude X″ of the aircraft 12″. This elevation buffer D is typically 700′ or 1000′ during enroute navigation, and the alert would be given if X″-Y″≦D. As before, the red area would be indicated to be at a range Z and at a bearing corresponding to the direction of the obstruction 14 relative to the centerline of the aircraft 12″. Also as before, an audible signal may also be given if certain criteria are met.
In situation II, a conventional altitude display would typically just display a visual signal as the altitude X′ of the aircraft 12′ is greater, than the predetermined elevation buffer D from the height Y of the obstruction 14, by a first distance d1. In other words, X′−Y≦D+d1d1 is also typically 1000′. The aircraft 12′ would not be considered to be completely free of the obstruction 14, however, and for this reason the visual signal would be of a cautionary nature. The visual signal would typically be a yellow area, such as a spot or square, on the cockpit display. As such, ‘YELLOW’ indicates this range. As with the red areas, the yellow area would be indicated to be at a range Z and at a bearing corresponding to the direction of the obstruction 14 relative to the centerline of the aircraft 12′.
Finally, in situation I, a conventional altitude display would typically just display a visual signal as the altitude X′ of the aircraft 12′ is greater than the height Y of the obstruction 14 by not only the elevation buffer D and the first distance d1, but also by a second distance d2. In other words, X′−Y≦D+d1+d2. d2 is again typically 1000′. The aircraft 12 would be considered to be mostly free of the obstruction 14, however, and for this reason the visual signal would typically be a green area, such as a spot or square, on the cockpit display. Again, ‘GREEN’ indicates this range. As with the red and yellow areas, the green area would be indicated to be at a range Z and at a bearing corresponding to the direction of the obstruction 14 relative to the centerline of the aircraft 12.
At higher aircraft altitudes, no colored area, or a black area, would be indicated. Here, ‘NONE’ is shown in the figure to denote this range.
Such altitude displays are clearly useful for warning pilots of impending dangerous terrain. However, such systems fail to account for important factors such as the actual flight path of the aircraft. As a result, their accuracy may be less than desired. For example, if an aircraft is climbing, the above described prior art altitude display may report a red area where one is not warranted. In the same way, if an aircraft is high but descending, the above-described prior art altitude display may display a green area where a red area is warranted.